Our goal is to improve the clinical usefulness of glycoprotein markers of cancer (of which CEA is the prototype) by elucidating the key role of the liver in regulating levels of circulating glycoproteins and defining the mechanisms by which Kupffer and hepatic cells clear them. We seek a clinically useful means for reversibly inhibiting this clearance and raising levels. This will make possible earlier cancer detection as well as improved monitoring of treatment. We have studied patients with very high CEA levels (from 12,000 to over 200,000 ng/ml) and have shown that their CEA is cleared slowly by rat liver. In contrast to other CEAs, the CEAs of these patients tend to have approximately 2-3 times the sialic acid content with a reduced fucose content. An immunochemical test for the clinical detection of the highly sialated CEAs from these patients is being developed utilizing isoelectric focusing in agarose, electroblot transfer to nitrocellulose, and detection by specific antibody and immunoperoxidase staining. Monoclonal antibodies specific for the high and low sialic acid CEAs are being produced. The presence of the markedly elevated CEA levels associated with slow CEA clearance has potential clinical use in earlier detection, prognosis, response, and resistance to chemotherapy. A CEA-binding protein has been isolated from rat Kupffer cells and we are producing monoclonal antibodies to this protein. We have shown impairment of CEA clearance by circulating bile acids and are studying the mechanism as well as the possible use of bile acids to reversibly inhibit clearance in patients. A non-CEA marker for "undifferentiated" cancer is being sought using established colon cancer lines and a new undifferentiated colon cancer cell line (MIP101), which has been obtained from fresh biopsy tissue of a human colonic cancer and grown both in culture and in nude mice. The undifferentiated nature of MIP101 has been confirmed by ultrastructural analysis. It produces no CEA and should prove useful in our search for an undifferentiated cancer marker. Monoclonal antibodies are being screened using a battery of malignant tissues and cells. Two antibodies which are specific for undifferentiated colon cancer have been found and are being developed for clinical use. (1)